4.0 to 5.0 are usually considers tremors.  5.0 to 6.0 as 'did you feel
that?' unless you own a liquor store right on top of the epicenter.  A 6.0
will break stuff if it hits just right, and will splash the water out of
swimming pools for a ways around.  6.0 to 7.0 will cause damage.  Again
depends on where and how much.  The 1994 California Northridge was 6.5.
Anything over 7.0 will cause massive damage.

Now here is where it gets tricky.  A 4.0 quake is considered the = of 1,000
tons of tnt.  A 5.0 is = 32,000 tons.  A 6.0 is 1 million tons.  A 7.0 is
32 million tons.  And 8.0 is 1 billion tons.

So the 1994 Alaska quake at 8.5 was a true monster.

Jo

Hi Nann
A 5.2 is definitely a quake.  It shakes everyone up wondering if it is
a pre-quake to a big one (something that usually happens about 6
months before a bigger quake).  Our Loma Prieta Quake which killed
many  people and collapsed bridges, was a 6.9.  A 5.2 can do much
damage (however, since every building here is retrofitted since the
Loma quake and everything not structurally sound went down then, we
don't see much physical damage in a 5.2).After a 5.2 when you finish
reassuring the neighborhood,  everyone calls friends,  checks water
supplies, and make sure the gas wrench is in place.

I can't even imagine a quake the size of the new Madrid which was
possible close to a 9(no Richter scale or way to measure then, so we
estimate)  I have been to devastating earthquakes that have killed
hundreds and thousands and  still been in the 7's.  The Hokkaido quake
was I think, an 8.2 and the results of that one were beyond belief. El
Salvador and mexico were in the7.6 or 7.7 range and those were
unbelievable destructive.  Northridge was just a 6.7 and I was stunned
at the amount of physical damage.

Well, I am sure telling my family in Misssouri to get some earthquake
supplies together and get them out of the house  (my family stores
disaster supplies in the basement (tornado land) which makes them
impossible for earthquakes.